Preheat the oven to 200ºC, fan 180ºC, gas mark 6. Heat the oil in a large frying pan over a medium heat. Add the onion and cook for 5 minutes, until softened, then add the garlic and herbs and cook for a further minute.
Add the mince and cook for a further 6-7 minutes, or until browned. Stir in the tomato purée, passata and chorizo (reserving a handful for the topping) and simmer for 5 minutes.
Spoon 1/3 of the beef mixture into a 20cm square ovenproof dish. Cover with 3 sheets of pasta and then 1/3 of the white sauce. Repeat, finishing with the white sauce and then sprinkle over the grated cheese and reserved chorizo. Bake in the oven for 35-40 minutes, until golden brown and bubbling. Serve with a fresh salad.